This invention relates to photography and particularly to a novel magenta coupler and their use in color photography.
It is well known that in color development the exposed silver halide in a silver halide emulsion layer oxidizes the primary aromatic amino developing agents, and the resulting oxidized products react with couplers to form dyes, thus resulting in formation of color images.
The role played by a coupler in color photography based on chromogenic development is very important and the stability of the color image, which is an important factor in color photography, depends largely on the couplers. For this reason, couplers and the dyes formed therefrom must generally meet a number of requirements.
Magenta couplers are required to satisfy particularly the following conditions:
(1) The coupler must be easily soluble in high-boiling solvents such as dibutyl phthalate and tricresyl phosphate and dispersible in the silver halide emulsion by use of a small amount of the solvent.
(2) The coupler remaining in the photographic material after the developing treatment must not turn yellow by the action of light, moisture, or heat, leaving stains on the photographic material.
(3) The coupler must have a high chromogenic efficiency, forming a magenta dye of high color density.
(4) The magenta dye formed from the coupler on chromogenic development must have such spectral absorption characteristics that the secondary absorption in blue ray region is low and the flank to the longer wavelengths in the absorption curve is steep.
(5) The magenta dye formed must be stable to light, moisture, and heat, permitting long storage without significant discoloration or fading.
Most of the conventionally known magneta couplers of the protected type are pyrazolone derivatives which are classified broadly into four groups of 1-aryl-3-alkyl-5-pyrazolones, 1-aryl-3-acylamino-5-pyrazolones, 1-aryl-3-ureido-5-pyrazolones, and 1-aryl-3-anilino-5-pyrazolones. Of these, 1-aryl-3-anilino-5-pyrazolones yield magenta dyes most excellent in spectral absorption characteristics which are the most important factor in color reproduction. As compared with the magenta dyes formed from other groups of pyrazolone derivatives, that obtained from 1-aryl-3-anilino-5-pyrazolones show the principal wavelength absorption maximum at somewhat shorter wavelength; smaller secondary absorption; and particularly smaller unnecessary absorption in the red ray region of longer wavelengths. Most of the dyes of this type, however, tend to fade when exposed to moisture and heat. Such defects have been improved in the 1-aryl-3-anilino-5-pyrazolone couplers having an alkoxy or halogen substituent at ortho-position with respect to the anilino group, which have been proposed by British Patent No. 956,261. The coupler of this type has advantages in that the magenta dye formed has a good fastness and a high color density owing to a high chromogenic efficiency of the coupler. Among such couplers, those represented by the following general formula have been used as the protected-type couplers. ##STR2## wherein L represents a halogen atom, an alkoxy group, or an alkyl group, A.sub.1 CO represents an acyl group, and A.sub.2 represents an aryl group.
In order to make a coupler usable as the protected-type coupler which is dissolved in a high-boiling solvent and dispersed in the silver halide emulsion, it is necessary to introduce into the coupler an oil-soluble and non-diffusing group having 8 or more carbon atoms. As the non-diffusing and oil-soluble group, certain substituted phenoxyalkyl groups have been proposed by U.S. Pat. Nos. 2,423,730, 2,474,293, and 2,908,573. It has been known that alkylphenoxyalkyl groups such as, for example, .alpha.-(2,4-di-tert-pentylphenoxy)-propyl group and .alpha.-(3-pentadecylphenoxy)propyl group are useful for magenta couplers of the pyrazolone type. However, as described hereinafter the 1-aryl-3-anilino-5-pyrazolone derivatives obtained by introducing these non-diffusing oil-soluble groups into the pyrazolones of the above formula have high melting points and low solubilities or, even if melting points are low, tend to crystallize in the emulsion layer. For these reasons, such derivatives of the 1-aryl-3-anilino-5-pyrazolones are not suitable for practical use as the protected-type coupler.